The present invention relates to a fuel injector of an internal combustion engine, and particularly to the improvement in the shape of an orifice nozzle tip of the fuel injector.
In recent years, there have been proposed and developed various swirl-type DI fuel injectors suited to direct-injection (DI) gasoline engines. One such swirl-type DI fuel injector has been disclosed in SAE Paper 2000-01-1045. The swirl-type DI fuel injector often uses a swirler located upstream of a conically or semi-spherically ended needle valve in order to give rotational momentum to fuel. FIG. 14 shows an L-cut orifice nozzle disclosed in the SAE Paper 2000-01-1045. As seen in FIG. 14, an axis of nozzle hole (orifice) 4 of the L-cut orifice nozzle is identical to an axis 24 of a substantially cylindrical nozzle body 6. The L-cut orifice nozzle tip (hereinafter is referred to as a xe2x80x9cprojected portion 20xe2x80x9d) is semi-cylindrical in shape and has a pair of rectangular flat wall surfaces (22a, 22b) parallel to the orifice axis identical to axis 24 of the nozzle body. In the fuel injector with the L-cut orifice nozzle disclosed in the SAE Paper 2000-01-1045, by means of the swirler the rotational momentum is given to the fuel in the orifice, so that the fuel flows or rotates in the circumferential direction of the nozzle hole.
As shown in FIG. 13, fuel is injected or sprayed from the nozzle hole of the L-cut orifice nozzle at a so-called fuel-flow angle (simply, a flow angle xcfx86) between a plane normal to the orifice axis and the direction of fuel flow as viewed from the vertical cross section. Flow angle xcfx86 is based on both an axial fuel flow velocity component W in the orifice-axis direction and a circumferential fuel flow velocity component U in the circumferential direction of nozzle hole 4 (exactly, rotating or swirling fuel flow direction), and defined or represented by the following expression (1).
xcfx86=tanxe2x88x921(W/U)xe2x80x83xe2x80x83(1)
On the other hand, a spray angle xcex1 of the fuel is also based on both axial fuel flow velocity component W in the orifice-axis direction and circumferential fuel flow velocity component U in the circumferential direction of nozzle hole 4, and represented by the following expression (2).
xcex1=2 tanxe2x88x921(U/W)xe2x80x83xe2x80x83(2)
Therefore, the relationship between flow angle xcfx86 and spray angle xcex1 is represented as the following expression (3).
xcfx86=90xc2x0xe2x88x92(xcex1/2)xe2x80x83xe2x80x83(3)
FIG. 15 shows the spray pattern of fuel injected from nozzle hole 4 with flow angle xcfx86 and spray angle xcex1. As can be seen from the spray shape shown in FIG. 15, a first collected fuel portion Xc and a second collected fuel portion Yc are produced. In FIG. 15, a plurality of arrows indicate directions of fuel injection (that is, swirling-fuel-flow direction). As seen from the perspective view shown in FIG. 14, on the assumption that a reference plane is a plane normal to the orifice axis and cutting a section of projected portion 20 that a height h of projected portion 20 measured in the orifice-axis direction relatively becomes smallest, and an intersection point between a central axis of the nozzle hole (i.e., the orifice axis) and the reference plane (h=0) is chosen as an origin O, an angle xcex8 is measured in a circumferential direction from a directed line radially extending from the origin O and including the intersection of the reference plane and rectangular wall surface 22a of the semi-cylindrical orifice nozzle tip. The height h of projected portion 20 at a certain angular position is axially measured from the reference plane. In the L-cut orifice nozzle, as shown in the fuel-spray angle characteristic shown in FIG. 16, spray angle xcex1 varies depending on angle xcex8. The spray pattern shown by the spray section of FIG. 15 is described in detail in reference to FIGS. 17-19. FIG. 17 shows a developed shape of semi-cylindrical projected portion 20 (the orifice nozzle tip facing the combustion chamber) in a xcex8-h coordinate system corresponding to a cylindrical coordinate system in which a xcex8-axis represents angle xcex8 measured in the circumferential direction from the previously-noted directed line, whereas an h-axis represents height h of projected portion 20 at a certain angular position. As can be seen from the developed shape of semi-cylindrical projected portion 20 shown in FIG. 17 by way of the xcex8-h coordinate system, the fuel is injected or sprayed out of the nozzle hole at the flow angle xcfx86 as indicated by the arrows P, Q, and R, but part of the fuel tends to impinge on rectangular flat wall surface 22b of the orifice nozzle tip (see the arrow Q of FIG. 17). As explained in more detail in reference to FIGS. 18 and 19, fuel sprayed through a first zone a of nozzle hole 4 produces a fuel spray within an angular range A. Fuel sprayed through a second zone b of nozzle hole 4 impinges on rectangular flat wall surface 22b and then flows along the wall surface. As a result of this, second collected fuel portion Yc (see FIG. 15) is produced in the direction substantially parallel to rectangular flat wall surface 22b and indicated by the arrow B. Fuel passing through a third zone o of nozzle hole 4 flows along the inner peripheral wall surface of semi-cylindrical projected portion 20, and then sprayed through a section f of the tip end of projected portion 20, and thus produces a fuel spray within an angular range F. Fuel passing through a fourth zone d of nozzle hole 4 flows along the inner peripheral wall surface of semi-cylindrical projected portion 20, and then sprayed out in the direction indicated by the arrow G. Owing to the fuel sprayed out in the direction indicated by the arrow G, first collected fuel portion Xc (see FIG. 15) is produced. In contrast, there is no fuel sprayed through a section e of the tip end of projected portion 20. When the fuel evaporates in the first collected fuel portion Xc, a comparatively rich air/fuel mixture results. For this reason, locating a spark plug at a position corresponding to first collected fuel portion Xc carries the advantage of reducing fuel consumption and emissions. That is, by way of better setting of the spark plug to the position corresponding to first collected fuel portion Xc, it is possible to efficiently feed the lowest possible fuel required in a lean or ultra-lean stratified combustion mode to the spark plug. This enhances the combustion stability in the stratified combustion mode.
As discussed above, in the conventional swirl-type DI fuel injector disclosed in the SAE Paper 2000-01-1045, it is possible to enhance an ignitability owing to the formation of first corrected fuel portion Xc, however, second corrected fuel portion Yc is simultaneously formed at an angular position spaced apart from the angular position of first corrected fuel portion Xc by the fuel impinging on and rebounded from rectangular flat wall surface 22b of the semi-cylindrical orifice nozzle tip (projected portion 20). The two corrected fuel portions Xc and Yc tend to form a denser air/fuel mixture, thus increasing unburned hydrocarbons (HCs). First corrected fuel portion Xc brings the advantage enhancing the ignitability, whereas second corrected fuel portion Yc never offers the benefit of enhanced ignitability. That is, second corrected fuel portion Yc merely causes unburnt HC emissions.
Accordingly, it is an object of the invention to provide a fuel injector of an in-cylinder direct-injection (DI) gasoline engine, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a swirl-type DI fuel injector of a DI gasoline engine, which is capable of achieving an excessively wide stratified combustion air-fuel ratio (AFR) zone and reduced fuel consumption and emissions (or improved emission control performance).
In order to accomplish the aforementioned and other objects of the present invention, a fuel injector of an internal combustion engine comprises a nozzle body having a nozzle hole formed in a tip of the nozzle body and a valve seat formed in the nozzle body upstream of the nozzle hole, a needle valve movable in a direction of an axis of the nozzle body to open and close the nozzle hole by moving the needle valve apart from the valve seat and by seating the needle valve on the valve seat, a swirler located upstream of the valve seat to give rotational momentum to fuel to be injected from the nozzle hole and to create swirling fuel flow, a projected portion whose inner peripheral wall is continuous with an inner peripheral wall surface of the nozzle hole, the projected portion being formed on an edge portion of an opening end of the nozzle hole so that a height of the projected portion, measured in a direction of an orifice axis of the nozzle hole, varies along a circumferential direction of the nozzle hole, the projected portion comprising a first sloped portion having a sloped surface that a height h1 of the sloped surface, measured in the orifice-axis direction, is dimensioned to gradually increase along a direction of the swirling fuel flow, and a second sloped portion having a sloped surface that a height h2 of the sloped surface, measured in the orifice-axis direction, is dimensioned to gradually decrease along the swirling-fuel-flow direction, a gradient of the sloped surface of the first sloped portion being defined by dh1/dxcex8 and a gradient of the sloped surface of the second sloped portion being defined by dh2/dxcex8, in a xcex8-h coordinate system corresponding to a cylindrical coordinate system in which a reference plane is defined as a plane normal to the orifice axis and cutting a section of the projected portion that the height of the projected portion becomes smallest, an intersection point between the orifice axis and the reference plane is chosen as an origin, an angular position of a point of the edge portion of the opening end of the nozzle hole with respect to the origin serving as a reference is represented by an angle xcex8 ranging from 0xc2x0 to 360xc2x0, the height of the projected portion in the orifice-axis direction with respect to the reference plane serving as a reference is represented by a height h, a xcex8-axis representing the angle xcex8 is taken as an axis of abscissa, and an h-axis representing the height h is taken as an axis of ordinate, and the projected portion being dimensioned to satisfy an inequality:
|dh1/dxcex8|max less than |dh2/dxcex8|max
where |dh1/dxcex8|max is an absolute value of a maximum value of the gradient of the sloped surface of the first sloped portion, and |dh2/dxcex8|max is an absolute value of a maximum value of the gradient of the sloped surface of the second sloped portion.
According to another aspect of the invention, a fuel injector of a gasoline direct-injection internal combustion engine comprises a nozzle body having a nozzle hole formed in a tip of the nozzle body and a valve seat formed in the nozzle body upstream of the nozzle hole, a needle valve movable in a direction of an axis of the nozzle body to open and close the nozzle hole by moving the needle valve apart from the valve seat and by seating the needle valve on the valve seat, a swirler located upstream of the valve seat to give rotational momentum to fuel to be injected from the nozzle hole and to create swirling fuel flow, a substantially cylindrical-hollow projected portion whose inner peripheral wall is parallel to an orifice axis of the nozzle hole and is continuous with an inner peripheral wall surface of the nozzle hole, the projected portion being formed on an edge portion of an opening end of the nozzle hole so that a height of the projected portion, measured in a direction of the orifice axis corresponding to the nozzle-body axis, varies along a circumferential direction of the nozzle hole, the projected portion comprising a first sloped portion having a sloped surface that a height h1 of the sloped surface, measured in the orifice-axis direction, is dimensioned to gradually increase along a direction of the swirling fuel flow, the first sloped portion sloping up from a first angular position to a second angular position advanced in the swirling-fuel-flow direction relative to the first angular position moderately at a gradient less than a flow angle xcfx86 of fuel injected from the orifice nozzle, the flow angle xcfx86 between a plane normal to the orifice axis and a fuel-flow direction as viewed from a cross section of the orifice-axis direction being defined by an expression xcfx86=tanxe2x88x921(W/U), where W is an axial fuel flow velocity component in the orifice-axis direction and U is a circumferential fuel flow velocity component in the circumferential direction of the nozzle hole, and a second sloped portion having a sloped surface that a height h2 of the sloped surface, measured in the orifice-axis direction, is dimensioned to gradually decrease along the swirling-fuel-flow direction, the gradient of the sloped surface of the first sloped portion being defined by dh1/dxcex8 and a gradient of the sloped surface of the second sloped portion being defined by dh2/dxcex8, in a xcex8-h coordinate system corresponding to a cylindrical coordinate system in which a reference plane is defined as a plane normal to the orifice axis and cutting a section of the projected portion that the height of the projected portion becomes smallest, an intersection point between the orifice axis and the reference plane is chosen as an origin, an angular position of a point of the edge portion of the opening end of the nozzle hole with respect to the origin serving as a reference is represented by an angle xcex8 ranging from 0xc2x0 to 360xc2x0, the height of the projected portion in the orifice-axis direction with respect to the reference plane serving as a reference is represented by a height h, a xcex8-axis representing the angle xcex8 is taken as an axis of abscissa, and an h-axis representing the height h is taken as an axis of ordinate, and the projected portion being dimensioned to satisfy an inequality:
|dh1/dxcex8|max less than |dh2/dxcex8|max
where |dh1/dxcex8|max is an absolute value of a maximum value of the gradient of the sloped surface of the first sloped portion, and |dh2/dxcex8|max is an absolute value of a maximum value of the gradient of the sloped surface of the second sloped portion.